This invention relates to an arrangement for open-end friction spinning wherein two rollers are arranged next to one another, form a wedge-shaped gap and are drivable in the same rotational direction by means of a joint driving belt that is looped around a pulley arranged on a shaft of an electric motor.
German DE-OS No. 28 10 184 discloses an arrangement wherein two rollers are mounted on shafts by means of roller bearings at each end of the shafts, and the shafts are provided with pulleys driven by a joint driving belt that is looped around a pulley of a stationary electric motor. In practice, this type of belt drive requires additional tensioning elements in order to ensure sufficient tension of the belt so that the two rollers are driven uniformly.
One of the objectives of the present invention is to provide an arrangement related to the previously mentioned type with a simplified construction and more operationally efficient drive.
This objective is achieved by running the driving belt along the surfaces of the rollers, and by mounting the electric motor in a guide in such a way that the motor is displaceable while maintaining the motor shaft in essentially parallel relation relative to the roller shafts.
By running the drive belt directly along the surfaces of the rollers, a significant simplification of the drive and of the bearings of the rollers is achieved because additional pulleys are not required. The surfaces of the rollers can be disposed on stationarily arranged shafts. The movable guide of the electric motor also makes it possible to tighten the driving belt in such a way that the correct tension of the belt can be adjusted without additional tightening or guiding means for the driving belt. This results in a drive with a very simple construction.
In a further development of the invention, the rollers and the electric motor are arranged at the vertices of a triangle. This results in a development which is advantageous with respect to space and ensures that both rollers and also the pulley of the electric motor are looped by the driving belt over a relatively large angle so that work can take place with a relatively low belt tension.
In a further development of the invention, the electric motor is mounted on a pivotal shaft that is parallel to the roller shafts. The result is a very simple guide means for the electric motor which ensures that the shaft of the electric motor may be displaced, but only in a manner maintaining the shaft parallel with respect to the roller shafts.
In a further development of the invention, the shaft of the electric motor is arranged outside a plane bisecting the wedge-shaped gap and closer to the roller following the electric motor in the running direction of the driving belt. Thus the circumstance is taken into account that the pulling end of the driving belt is loaded with a higher tensile force than the other end, whereas, the shafts of both rollers are loaded approximately equally.
In a further development of the invention, it is provided that the guide for the electric motor is mounted on a bearing support which also supports the shafts of the rollers. As a result, the rollers and their drive are combined into one structural unit. It is therefore possible to align the rollers and their drive including the electric motor precisely with one another without excessive cost.
In order to adjust the tension of the belt to a desired magnitude, in a further development of the invention the electric motor is loaded by one or more biasing means. The biasing means are designed taking into account the position in which the electric motor is installed. When the shafts of the rollers and shaft of the electric motor are horizontally arranged, the weight of the electric motor itself may suffice as a biasing force, and if necessary, may be partially alleviated by a spring. In the case of a vertical arrangement of the shafts of the rollers and of the shaft of the electric motor, a spring biasing means alone must produce the tension in the belt.
In a further development of the invention, the path of the electric motor in its guide is limited by one or several limit stops. This prevents uncontrolled displacement of the driving motor in the case of a breakage of the driving belt.
In a further development of the invention, devices are provided for switching off the electric motor which respond to a breakage of the driving belt and/or a fault detected in spun yarn. This prevents the driving motor or the rollers from being damaged in the case of a problem, whether it is a breakage of the driving belt or of the yarn.
In a further development of the invention, means are provided for adjusting the position of the driving motor in order to change the tension of the driving belt. In this case, it is particularly advantageous to provide means to increase the tension of the driving belt temporarily when the rollers are started during a yarn piecing process so that slippage of the driving belt over the cylindrical surfaces of the rollers decreases and a shorter acceleration time to operational angular velocities is reached.
In a further development of the invention, braking means are provided that can be applied to the surfaces of the rollers. Braking means of this type are especially advantageous for an automatic yarn piecing process.
In a further development of the invention, it is provided that means for changing the tension of the driving belt and braking means are coupled with one another in such a way that the tension of the driving belt is decreased when the braking means are actuated. This prevents the full driving capacity from being transferred to the rollers during braking so that the brakes as well as the drive are preserved.
In a further development of the invention, one or more roller bearings are disposed on the roller shafts under the surfaces of the rollers in the area where the driving belt and/or the braking means are applied. This ensures that the forces that are applied to the surfaces of the rollers from the outside are transferred as directly as possible into the bearings and shafts.
In a further development of the invention, the electric motor has an acceleration curve that rises at a flat angle and a braking curve that decreases at a flat angle. This development has the advantage that starting as well as stopping takes place relatively gently without any additional measures so that considerable slippage is avoided between the driving belt and the roller surfaces at the time of starting and at the time of stopping the rollers.
Further objects, advantages and novel features of the present invention will become more apparent from the following detailed description when considered in conjunction with the accompanying drawings which show, for purposes of illustration only, embodiments in accordance with the present invention.